1. Field of the Invention
The present invention relates to a data collection scheme, and more particularly, to a method and a system for collecting data from unspecified number of many terminals to a center through a public network efficiently, by fully utilizing a processing capacity of center service ports, without exerting unnecessary processing load on the public network.
2. Description of the Background Art
A conventional data collection system has a schematic configuration as shown in FIG. 1, which comprises a center 10, a plurality of terminals 20, and a public network 30 by which the center 10 and the terminals 20 are connected. The center 10 receives data from individual terminals 20, and collects these data together as a collected data. The terminals 20.sub.1 to 20.sub.n transmit the data to the center 10 through the public network 30.
Here, the center 10 has an internal configuration as shown in FIG. 2, which comprises a plurality of data reception units 11, a data collection unit 12 connected with the data reception units 11, and a collected data transmission unit 13 connected with the data collection unit 12. The data reception units 11.sub.1 to 11.sub.n receive data arriving from the individual terminals 20 through the public network 30. The data collection unit 12 collects the data obtained by the data reception units 11.sub.1 to 11.sub.n together. The collected data transmission unit 13 transmits the collected data obtained by the data collection unit 12.
On the other hand, each terminal 20 has an internal configuration as shown in FIG. 3, which comprises a terminal data input unit 21, a terminal data storage unit 22 connected with the terminal data input unit 21, a terminal data transmission unit 23 connected with the terminal data storage unit 22 and a communication line of the public network 30, a busy line handling unit 24 connected with the communication line connected to the terminal data transmission unit 23, and a calling operation command unit 25 connected with the terminal data storage unit 22, the terminal data transmission unit 23, and the busy line handling unit 24.
The terminal data input unit 21 enters data into the terminal 20. The terminal data storage unit 22 stores the data entered from the terminal data input unit 21 until the transmission of the data is completed. The terminal data transmission unit 23 calls up the center 10 through the public network 30, and transmits the data stored in the terminal data storage unit 22. The busy line handling unit 24 judges whether the line is connected as a result of the calling from the terminal data transmission unit 23, and controls the calling operation command unit 25 to repeat the calling operation when the line is busy. The calling operation command unit 25 activates the calling operation at the terminal data transmission unit 23.
In this configuration of FIG. 3, the data entered from the terminal data input unit 21 is stored in the terminal data storage unit 22. When the storing of the data to be transmitted is completed, the terminal data storage unit 22 notifies the calling operation command unit 25 that the data is ready for transmission, and await for a timing to supply the data to the terminal data transmission unit 23. The calling operation command unit 25 issues a command for calling to the terminal data transmission unit 23 when a timing for calling is given. When this call command is received from the calling operation command unit 25, the terminal data transmission unit 23 calls up the center 10 through the public network 30, and when the line is successfully connected, the terminal data transmission unit 23 reads out the data stored in the terminal data storage unit 22 and transmits the data to the center 10 through the public network 30. The busy lie handling unit 24 monitors a state of the communication line connected to the terminal data transmission unit 23, and when a busy line state is detected in response to the calling from the terminal data transmission unit 23, the busy line handing unit 24 notifies a need of re-calling to the calling operation command unit 25.
In this terminal 20 of FIG. 3, the calling operation command unit 25 and the busy line handling unit 24 have internal configurations as shown in FIG. 4, where the calling operation command unit 25 has a wait time determination unit 251 for determining a wait time until the calling, while the busy line handling unit 24 has a busy state detection unit 241 for checking whether the communication line is in a busy state or not in response to the calling, and a re-calling command unit 242 for notifying a need of re-calling due to the busy line to the calling operation command unit 25.
When a notice from the terminal data storage unit 22 indicating that the data is ready for transmission is received, the wait time determination unit 251 of the calling operation command unit 25 determines an appropriate time interval, and issues the call command to the terminal data transmission unit 23 after awaiting for the determined time interval. Subsequently, when the busy state detection unit 241 of the busy line handling unit 24 detects the communication line in the busy state, and a notice from the re-calling command unit 242 of the busy line handling unit 24 indicating the need of re-calling is received, the wait time determination unit 251 of the calling operation command unit 25 determines an appropriate time interval again, and issues the call command to the terminal data transmission unit 23 again after awaiting for the determined time interval.
In this conventional data collection system, the center 10 does not have a list of addresses of individual terminals 20, so that the center 10 cannot collect the terminal data by the polling from the center 10 side in a case of collecting unspecified number of many terminal data, and it is necessary for each terminal 20 to call up the center 10 through the public network 30. However, conventionally, there has been no way of notifying how busy the center 10 is to unspecified number of many terminals, so that each terminal 20 calls up the center 10 through the public network 30 according to its own convenience, totally unsystematically.
Now, when many terminals call up the center in excess to a processing capacity of the center service ports, it becomes necessary for the network to carry out the call loss processing with respect to the overflowing calls, so that a processing load due to a processing which is not directly related to the data transmission and reception will be exerted on the network.
For this reason, each terminal 20 has a locally predetermined wait time interval, such that the calling operation is repeated at this wait time interval until the call is connected. However, in this conventional scheme, it is necessary for each terminal 20 to have a locally predetermined wait time interval, and besides, each local terminal 20 cannot know a total number of terminals which are potentially trying to call up the center 10, so that it is difficult to control a total number of calls which are simultaneously made from a number of terminals 20 to a level close to a processing capacity of the center service ports. In other words, it is difficult to control this total number of calls at a level which can fully utilize the processing capacity of the center service ports while not exerting any extra processing load on the network.
On the other hand, unless the center service ports are operated near their processing capacity limit, the data collection time becomes long. On the contrary, when the processing capacity of the center service ports is exceeded considerably to exert the extra processing load to the network, it becomes impossible for the network to concentrate on the connection processing related to the data collection, and for this reason the data collection time also becomes long.